Two senior figures in Boris Johnson's Mayor's Office for Policing and Crime (MOPC) have left suddenly, less than a month before the start of the London Olympic Games.

Catherine Crawford, the chief executive of MOPC and who was previously chief executive of the now defunct Metropolitan police authority (MPA), retired after 12 years and left on Friday. Her deputy, Jane Harwood, also left the same day but no reason has been given for her departure.

The email stated: "We are very sorry that it has not been possible to see all of you face-to-face to tell you that today is our last day in the office. The timing has been outside our control."

A spokesman for the mayor said they were seeking new appointments as soon as possible. But the departures without a handover period so close to the Games has raised eyebrows.

Johnson's deputy mayor for policing, Stephen Greenhalgh, who admitted to a City Hall meeting last month that he was "not an expert on operational policing matters" and had not been briefed on the Games, will be in overall charge of MOPC, and senior managers will look after the day-to-day working.

City Hall declined to comment on reports that the resignations were prompted by Greenhalgh because he wanted to work with a new team.

Joanna McCartney, Labour's City Hall police and crime spokeswoman, said she intended to raise the matter at the monthly mayor's question time on Wednesday, when assembly members quiz the mayor.

"It is deeply worrying that two of the most experienced senior managers have left the Mayor's Office for Policing and Crime," said McCartney.

"Boris Johnson has brought in a new deputy mayor for policing, Stephen Greenhalgh, who isn't on top of his brief yet. With the Olympics just four weeks away it is very concerning that the staff have left."

Caroline Pidgeon, a Liberal Democrat assembly member said on Twitter: "Shocking that 2 public servants with vast experience should go so quickly after new Deputy Mayor for Policing has started."

She added: "Given Deputy Mayor's performance to date you would have thought he would want to surround himself with experienced people."

Johnson praised Crawford, who moved from the MPA to MOPC when it took over the authority's functions in January.

In a statement, the Conservative London mayor, said: "Often working behind the scenes Catherine, has, over the years, commanded the respect of colleagues, senior police officers and cross-party politicians. I have personally valued her consistent advice and support and wish her well for the future.''

On Harwood, who joined the MPA in April 2008 before moving over to MOPC, Johnson said she had made a "huge contribution" through "her resilience, professionalism and extensive experience of policing and management".